1. Field of the Invention
The present invention relates to a touch panel, and more particularly, to a touch panel for a display device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing an electrostatic discharge.
2. Discussion of the Related Art
In order to efficiently use various electronic devices, touch panels have been widely used to input signals on display surfaces without additional remote controllers or other input devices. The touch panels have been widely integrated with display surfaces of flat display devices such as electronic calculators, liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescence (EL) devices, and cathode ray tubes (CRTs). By integrating the touch panels with display devices, a user can select desired information while watching an image displayed on the display device.
Depending upon a sensing method when a user touches a display surface, the touch panels may be classified into a resistive type, an electromagnetic type, a capacitor type, an infrared type, and a light sensor type.
Among the various type touch panels, the resistive type touch panel includes an upper transparent substrate having an upper electrode, and a lower transparent substrate having a lower electrode. The lower and upper transparent substrates are bonded to each other at a constant interval. Accordingly, if the surface of the upper transparent substrate is touched at a predetermined point using input means, e.g., a finger, a pen, and etc., the upper electrode formed on the upper transparent substrate is electrically connected to the lower electrode formed on the lower transparent substrate. A voltage change by a resistance value or a capacitance value of the touched point is then detected and output along with a location defined by coordinates of the touched point.
The related art analog resistive type touch panel will be described with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating how a signal is applied for the operation of the related art touch panel. As shown in FIG. 1, a touch panel 100 is positioned on an LCD device 130 having a backlight 140, in which transparent electrodes are formed on opposing surfaces of lower and upper substrates, and metal electrodes are formed for providing signal voltages to the transparent electrodes according to the X-axis and Y-axis directions. Then, the electrodes are connected to a touch panel controller 110 for applying the signal voltages to the metal electrodes of the touch panel 100, or reading the voltage of a touching point. Also, the touch panel controller 110 is connected to a micro-computer 120 for controlling the entire system including a display device.
Hereinafter, a touch panel for an LCD device according to the related art will be described with reference to the accompanying drawings.
FIG. 2 is a plane view schematically illustrating the related art touch panel. FIGS. 3A and 3B are plane views illustrating metal electrodes and signal applying line application on respective upper and lower substrates of FIG. 2. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2. FIG. 5 is a cross-sectional view taken along line V-V of FIG. 2. FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 2.
As mentioned above, the related art touch panel for the display device is used as a means for inputting signals on the display surface of the LCD device. Referring to FIG. 2, the related art touch panel for the display device includes a viewing area corresponding to the display surface of the display device, and a dead space region 20 corresponding to the circumference of the viewing area surrounding the viewing area. With this configuration, the upper and lower transparent substrates are bonded to each other through an insulating adhesive provided in the dead space region 20. That is, rectangular upper and lower PET (polyethylene terephtalate) substrates 1 and 2 corresponding to the display surface of the display device are formed to face into each other, and then first and second transparent electrodes 3 and 4 are respectively formed on the upper and lower PET substrates 1 and 2. Then, the upper and lower PET substrates 1 and 2 are bonded to each other by the insulating adhesive provided in the dead space region 20 at a predetermined interval.
Accordingly, if a predetermined portion of the upper PET substrate 1 is touched with a pen or a finger, the first and second transparent electrodes 3 and 4 are also electrically connected to each other at the predetermined portion, so that a voltage, varied by a resistance or a resistance value of the touching point, is detected and output. In order to detect the voltage output by the resistance value or the capacitance value at the predetermined portion, a signal applying line is connected to apply a voltage to the first and second transparent electrodes 3 and 4, and to read the voltage value varied by the touching point. The signal applying line is connected to the first and second transparent electrodes 3 and 4 in the dead space region 20.
The related art touch panel for the display device will be explained in more detail with reference to the plane and cross-sectional views described below.
Referring to FIGS. 3A and 3B, and FIGS. 4 to 6, the transparent upper and lower PET substrates 1 and 2 are formed to have a size and a shape corresponding to the display surface of the display device. The first and second transparent electrodes 3 and 4 are formed on each opposing surface of the upper and lower PET substrates 1 and 2. Then, metal electrodes (e.g., Ag paste) are formed in the dead space region 20. Referring to FIG. 3A, first and second metal electrodes 5a and 5b are formed in the dead space region 20 at the left and right sides of the upper PET substrate to be connected to the first transparent electrode 3. The first and second metal electrodes 5a and 5b are connected to first and second signal applying lines 5c and 5d directly connected to external power sources Vcc and Vss for applying voltage signals from the external.
Herein, as shown in FIGS. 4 and 5, the first and second metal electrodes 5a and 5b are electrically connected to the transparent electrode 3, so that the first and second metal electrodes 5a and 5b are directly formed on the transparent electrode 3. However, the second signal applying line 5d is electrically connected to the second metal electrode 5b, as shown in FIG. 4, and electrically insulated from the transparent electrode 3. In this respect, a first insulating layer 10a is formed between the transparent electrode 3 and the electrode having the second signal applying line 5d. As shown in the second signal applying line 5d, the first signal applying line 5c is directly connected to the first metal electrode 5a for applying the voltage signal, and an insulating layer is formed between the transparent electrode 3 and the electrode having the first signal applying line 5c. 
Accordingly, the first and second signal applying lines 5c and 5d are bonded to flexible printed cable (FPC) 7 at one portion of the substrate by a conductive adhesive 8a, so that the external voltage signals are applied to the first and second metal electrodes 5a and 5b through the first and second signal applying lines 5c and 5d. Also, as shown in FIG. 3B, third and fourth metal electrodes 6a and 6b are formed in the dead space region 20 at the lower and upper sides of the lower PET substrate 2 to be connected to the transparent electrode 4, and third and fourth signal applying lines 6c and 6d are formed in the dead space region 20 at the left side of the lower PET substrate 2 to be electrically connected the third and fourth metal electrodes 6a and 6b to the FPC 7. Referring to FIG. 4, as shown in the first and second signal applying lines 5c and 5d, a second insulating 10b is formed between the transparent electrode 4 and the signal applying line 6c to electrically insulate the signal applying line 6c from the transparent electrode 4. Also, the FPC 7 is connected to the third and fourth metal electrodes 6a and 6b in the dead space region 20 through the third and fourth signal applying lines 6c and 6d. 
The first and second signal applying lines 5c and 5d are printed on the upper surface of the FPC 7, and the third and fourth signal applying lines 6c and 6d are printed on the lower surface of the FPC 7. As shown in FIG. 6, the first, second, third, and fourth signal applying lines 5c, 5d, 6c, and 6d are bonded by the conductive adhesives 8a and 8b. The first to fourth signal applying lines 5c, 5d, 6c, and 6d printed on the upper and lower surfaces of the FPC 7 output the voltage to the transparent electrode 3 or 4 when applying the power supply voltage Vcc and the ground voltage GND to the first to fourth metal electrodes 5a, 5b, 6a, and 6b of the transparent electrode 3 or 4, or electrically connecting the upper and lower transparent electrodes 3 and 4 to each other at a predetermined portion.
As mentioned above, the first to fourth signal applying lines 5c, 5d, 6c, and 6d are bonded to the FPC 7 by the conductive adhesives 8a and 8b, and the upper and lower substrates 1 and 2 are bonded to each other in the dead space region without the FPC 7 by an insulating adhesive 9.
A method for electrically bonding the first to fourth signal applying lines 5c, 5d, 6c, and 6d to the FPC 7 will now be explained in detail. First, the conductive adhesive 8a is positioned below the first and second signal applying lines 5c and 5d bonded to the upper surface of the FPC 7, and the conductive adhesive 8b is positioned on the third and fourth signal applying lines 6c and 6d bonded to the lower surface of the FPC 7. Next, the insulating adhesive 9 is deposited in the dead space region 20 except for the portion of the dead space region occupied by the FPC 7. Subsequently, only the portion of the FPC 7 on which the conductive adhesive is formed is heated at a temperature of approximately 100° C., and pressed by the external force. Thus, the FPC 7 is bonded to the first to fourth signal applying lines 5c, 5d, 6c, and 6d, and the lower and upper substrates 1 and 2 are bonded to each other.
The operation of the touch panel for the display device according to the related art will be explained as follows.
If the surface of the upper substrate 1 is touched at the predetermined portion with a pen or a finger, the first and second transparent electrodes 3 and 4 become electrically connected to each other at the predetermined portion. Accordingly, the power supply voltage (Vcc) and the ground voltage (GND) are applied to the right and left sides of the first transparent electrode 3 formed on the upper PET substrate 1 through the two signal applying lines 5c and 5d printed on the upper surface of the FPC 7 and the metal electrodes 5a and 5b. A voltage, having a value varied by a resistance value or a capacitance value specific to the touch point, is then outputted through the second transparent electrode 4 of the lower PET substrate 2 and the metal electrodes 6a and 6b, and the two signal applying lines 6c and 6d printed on the lower surface of the FPC 7, so that the X-axis coordinates are detected.
Next, the power supply voltage Vcc and the ground voltage GND are applied to the upper and lower sides of the second transparent electrode 4 formed on the lower PET substrate 2 through the two signal applying lines 6c and 6d printed on the lower surface of the FPC 7 and the metal electrodes 6a and 6b. Then, the voltage value is then output at the touching point by the first transparent electrode 3 and the metal electrodes 5a and 5b of the upper PET substrate 1, so that the Y-axis coordinates are detected. Accordingly, the X-Y coordinates of the touching point are detected.
FIG. 7 illustrates an FPC, to which a signal applying line of the related art touch panel is bonded, to the rear side of a lower substrate in a display device. FIG. 8 is an expanded view of FIG. 7 illustrating a contact hole of the FPC. FIG. 9 is a cross-sectional view taken along line IX-IX of FIG. 8.
As mentioned above, as shown in FIG. 7, the FPC 7 and the first to fourth signal applying lines 5c, 5d, 6c, and 6d bonded to the upper and lower surfaces of the FPC 7 are bent to the side of the touch panel, and pass through the rear side 60 of an LCD panel integrated with the touch panel, so that the FPC 7 passes through a driver IC 51 connected to a printed circuit board (PCB). In this case, as shown in FIG. 8, the driver IC 51 may be in direct contact with the third and fourth signal applying lines 6c and 6d bonded to the lower surface of the FPC 7 among the signal applying lines bonded to the FPC 7, thereby causing a short-circuit of the driver IC 51. Especially, when performing a shock test for preventing an electrostatic discharge (ESD), a short-circuit of the driver IC is generated.
As shown in FIG. 8, the FPC 7 passing through the PCB 50 is connected to a touch panel controller (not shown) to input and output the signal voltage to the transparent electrode of the touch panel. A through-hole 55 is formed in the FPC 7 to facilitate a connection to the touch panel controller, so that the third and fourth signal applying lines 6c and 6d of the lower surface of the FPC 7 are formed to the upper surface of the FPC 7. However, as shown in FIG. 9 of a cross-sectional view taken along line IX-IX of FIG. 8 for illustrating a portion prior to forming the through-hole 55, the first and second signal applying lines 5c and 5d are formed on the upper surface of the FPC 7, and the third and fourth signal applying lines 6c and 6d are formed on the lower surface of the FPC 7. As a result, the third and fourth signal applying lines 6c and 6d formed on the lower surface of the FPC 7 may be in contact with the driver IC.
Accordingly, the related art touch panel for the display device has the following disadvantages.
In the related art touch panel for the display device, the FPC is formed to apply the signal to the metal electrodes on the transparent electrode. When the FPC is bent to the bottom of the LCD device, some of the signal applying lines bonded to the FPC may be in direct contact with the driver IC of the LCD device, so that the driver IC may be damaged during a shock test for preventing an electrostatic discharge (ESD).